1. Field of the Invention
The present invention relates to a pressure relief valve, and more particularly to a pressure relief valve, which mounts to a pressure accumulator (common rail) and other such pressure apparatus for a fuel supply system or fuel injection system of an internal combustion engine, such as a gasoline engine or diesel engine.
2. Description of the Related Art
A conventional pressure relief valve comprising a common rail and the like will be explained in general terms based on FIG. 7 and FIG. 8.
FIG. 7 is a simplified diagram of an example of a conventional internal combustion engine fuel injection system 1, the fuel injection system 1 having a fuel tank 2, a pressure pump 3, a common rail 4, a pressure relief valve 5, and an injector 6.
Pressure relief valve 5 functions as a safety valve for maintaining the pressure inside common rail 4 at less than a prescribed value, and, in addition, also functions as a pressure control valve when a pressure pump 3 control valve (not shown in the figure) malfunctions.
When this pressure relief valve 5 is mounted to common rail 4, the problem is that, in a conventional structure, the pressure relief valve 5 is long, jutting out lengthwise from the side of common rail 4, and, in addition, a completely sealed structure is difficult to achieve, the shape of the spring seat is complex, and it is costly.
FIG. 8 is a cross-sectional view of pressure relief valve 5, pressure relief valve 5 having a valve holder 7, a valve seat 8, a ball valve 9 (valve body), a spring seat 10, a valve spring 11, a sealing ball 12, and a filter 13.
Valve holder 7 has a high-pressure portion side end portion 7A, which faces the high-pressure portion side H of the inside of common rail 4, and a low-pressure portion side end portion 7B, which faces the low-pressure portion side L of the outside, and is integrated with valve seat 8 by a weld portion 14 in accordance with laser welding, and in a state, wherein valve spring 11 is housed on the inside thereof, the inside thereof is sealed by sealing ball 12, which is press-fitted from the low-pressure portion side end portion 7B.
Furthermore, valve holder 7 is fastened to common rail 4 by a snap ring 15, and the high-pressure portion side H of common rail 4 and the low-pressure portion side L of common rail 4 are sealed by a first O-ring 16.
Valve seat 8 forms a valve seat surface 17 in which ball valve 9 is seated, and when ball valve 9 is lifted from valve seat surface 17, the high-pressure portion side H is connected to the atmospheric-pressure fuel tank 2 side via a linking passage 18 of the high-pressure side of valve seat surface 17 and a radial passage 19 of the low-pressure side, enabling the circulating flow of high-pressure fuel.
A backup ring 20 and a second O-ring 21 are provided for valve seat 8, sealing the high-pressure portion side H and the low-pressure portion side L.
Spring seat 10 is inside valve seat 8, slides axially therein, and seats valve spring 11 between itself and sealing ball 12, and, in addition, causes ball valve 9 to make contact at a prescribed injection valve opening pressure with valve seat surface 17 of valve seat 8 in accordance with the biasing force of valve spring 11.
A flat cut 22 is formed axially in spring seat 10, enabling the linkage of the spring chamber 23 of valve spring 11 and the valve chamber 24 of ball valve 9.
In a pressure relief valve 5 of a constitution such as this, the pressure inside the high-pressure portion side H of the common rail 4 is extremely high, and when this pressure is greater than the injection valve opening pressure resulting from valve spring 11, ball valve 9 is lifted from valve seat surface 17 of valve seat 8 against the biasing force of valve spring 11, and pressure escapes from the high-pressure portion side H to the fuel tank 2 side via linking passage 18, valve chamber 24 and radial passage 19.
However, the problem is that valve holder 7 of pressure relief valve 5 juts out far from common rail 4, and, in addition, because spring chamber 23 of valve holder 7 is closed off or sealed by only sealing ball 12, there is the possibility of fuel leaking to the outside from spring chamber 23.
Furthermore, spring seat 10 has a complex shape, and, in addition, there is the possibility of radial external force acting on spring seat 10 in line with the operation of valve spring 11, raising concerns of unstable operation, and, in addition, the durability thereof is a problem.
Further, the problem is that the position of ball valve 9, which receives the flow of fuel, is unstable, and there is the likelihood that hunting will occur.
Pressure relief valves are disclosed in, for example, Japanese Patent Application Laid-open No. H9-105473, and Japanese Patent Application Laid-open No. H11-182242.
With the foregoing problems in view, it is an object of the present invention to provide a pressure relief valve in which the valve holder does not jut far out from the common rail.
Further, an object of the present invention is to provide a pressure relief valve in which a reliable sealing structure is achievable in the valve holder.
Further, an object of the present invention is to provide a pressure relief valve, which is capable of being manufactured at low cost, and is capable of being made compact.
Further, an object of the present invention is to provide a pressure relief valve, which facilitates adjustment of the injection valve opening pressure, and is capable of being manufactured at low cost.
Further, an object of the present invention is to provide a pressure relief valve, which simplifies the shape of the spring seat.
Further, an object of the present invention is to provide a pressure relief valve capable of guaranteeing the operational stability of the valve spring in the valve holder.
Further, an object of the present invention is to provide a pressure relief valve, which is capable of preventing hunting in a valve body, such as a ball valve, and, in addition, is capable of enhancing the wear resistance of a contact portion.
A first invention has been made, focusing on making the low-pressure portion side end portion of a valve holder a closed structure, and is a pressure relief valve, having a valve holder, which has a high-pressure portion side end portion facing the high-pressure portion side, and a low-pressure portion side end portion facing the low-pressure portion side; a valve spring, which is housed inside this valve holder; a spring seat on which this valve spring is seated; a valve seat, which is mounted to the above-mentioned valve holder; and a valve body, which, in accordance with the pressure of the fluid of the above-mentioned high-pressure portion side, is lifted from this valve seat against the biasing force of the above-mentioned valve spring, this pressure relief valve being characterized in that there is formed a closed end portion for making the above-mentioned low-pressure portion side end portion of the above-mentioned valve holder a closed state, and, in addition, the above-mentioned valve spring can be seated between the inner wall surface of this closed end portion and the above-mentioned spring seat.
The above-mentioned closed end portion can be made deformable towards the inside of the above-mentioned valve holder.
The above-mentioned valve seat can be press fitted to the above-mentioned valve holder, and, in addition, it is possible to provide a stopper step portion for determining a press fitting position between the above-mentioned valve seat and the above-mentioned valve holder.
In a pressure relief valve according to the first invention, because the low-pressure portion side end portion of the valve holder is constituted so as to be a closed structure, this closed structure differs from a sealing structure for sealing the inside of a valve holder using a sealing ball as in a conventional pressure relief valve, and makes it possible to reliably seal the inside of the valve holder, and to reliably prevent the leaking of fuel or other fluids to the outside.
Furthermore, by deforming the closed end portion, which is a closed structure, toward the inside of the valve holder, it is possible to adjust the biasing force of the valve spring, and to easily adjust the injection valve opening pressure as a pressure relief valve, and it is possible to contribute toward lowering costs.
Further, according to a second invention, which focuses on making the spring seat of the valve spring a cup shape, is provided a pressure relief valve, having a valve holder, which has a high-pressure portion side end portion facing the high-pressure portion side, and a low-pressure portion side end portion facing the low-pressure portion side; a valve spring, which is housed inside this valve holder; a spring seat on which this valve spring is seated; a valve seat, which is mounted to the above-mentioned valve holder; and a valve body, which, in accordance with the pressure of the fluid of the above-mentioned high-pressure portion side, is lifted from this valve seat against the biasing force of the above-mentioned valve spring, this pressure relief valve being characterized in that the above-mentioned spring seat is a cup-shaped spring seat, and is housed in a slidable condition inside the above-mentioned valve holder.
The above-mentioned cup-shaped spring seat can be provided at the opposite ends of the above-mentioned valve spring, respectively.
A valve plate, which is capable of moving axially in an integrated condition with the above-mentioned valve body, and, in addition, is capable of sliding radially relative to the above-mentioned cup-shaped spring seat, can be interposed between the above-mentioned cup-shaped spring seat and the above-mentioned valve body.
In a pressure relief valve according to the second invention, because the spring seat of the valve spring is made into a cup shape, it is possible to load the necessary biasing force onto the valve body without having a complex shape as in a conventional pressure relief valve, and the pressure relief valve can be made compact and low-priced, and, in addition, it is also possible to curb the receiving of radial external force in line with the operation of the valve body, making it possible to ensure reliability and stability as a pressure relief valve.
Furthermore, by providing a valve plate, which is capable of moving axially in an integrated condition with the valve body, and, in addition, is capable of sliding radially relative to the cup-shaped spring seat, it is possible to stably maintain the position of the valve body resulting from the flow of a fuel or other such fluid, to prevent hunting, and to stabilize operation, and, in addition, it is possible to enhance the wear resistance of the valve body contact portion.